1. Field of the Invention
The present invention relates to a tire for use on motor vehicles, trailers, motorcycles, aircraft or similar (referred to generally as xe2x80x9cvehiclesxe2x80x9d in the following text), provided with an electricity generator which can supply sensors and any other circuits incorporated in the said tire, the generator having no galvanic contact with fixed or rotating components present in the vehicle. In particular, the invention relates to a tire in which the unit formed by one part of the generator, the sensors and the bead wire constitutes an assembly to be incorporated in the carcass of the tire during its manufacture.
The invention also relates to a method for the manufacture of the said tire.
2. Description of the Related Art
The structure of an ordinary tire essentially comprises a carcass provided with at least one piece of reinforcing rubberized fabric, or carcass ply, each of whose edges is fixed to at least one circumferentially inextensible annular metal core, commonly known as the bead core, which is the reinforcing member which keeps the tire on its mounting rim. The carcass is completed by a pair of sidewalls, in axially opposing positions, and a tread strip disposed on the crown of the casing and impressed with a relief pattern which imparts to the tire particular qualities of behaviour in use. The tire can also be provided with a belt structure, normally produced with rubberized fabrics incorporating metal reinforcing cords, interposed between the carcass and the tread band.
Circuits comprising encoders and/or sensors, connected to transponders (which receive signals and transmit responses), supplied by induction, and housed within vehicle tires or wheels, have been known for some time.
For example, patent application WO 90/12474, having the title xe2x80x9cVehicle tire identification systemxe2x80x9d, describes a system consisting of a transponder located within a tire, supplied by a winding disposed in the crown portion of the tire, or at least situated in a position remote from the bead cores of the said tire (p. 5, lines 20-22).
This winding is supplied by induction with an alternating current of suitable frequency by means of a large excitation winding which is disposed outside the tire and carried by a scanning tool such as a bar, or located in a fixed place, for example in the road surface, and which is brought close to the equator of the tire where the said transponder supply winding is housed.
In the absence of information on this matter, the applicant considers that this arrangement remote from the bead cores is due to the necessity of preventing the reduction of the efficiency of the winding by parasitic currents which would be generated in the bead core by the inductive coupling between the bead core and a winding disposed in its vicinity. An advantage of the system described is the fact that the transponder supply winding, because of its dimensions, operates even if the winding of the scanning tool is not disposed in its immediate vicinity, whereas the latter arrangement is necessary if the supply winding has a small diameter and is situated in a closely defined point of the crown or of the sidewall of the tire.
However, the device proposed in patent application WO 90/12474 has at least the following drawbacks:
a) it requires transponder supply windings positioned close to the equator of the cover, in other words just under the tread band or in its immediate vicinity, to minimize the losses of efficiency of the said windings due to the presence of the bead cores. This greatly complicates the tire production process and has the further disadvantage of potential structural problems due to the presence of the winding in a part of the tire subject to considerable stresses and deformations when in use;
b) it necessitates the installation of the device using the power generated by the winding in the same highly mechanically stressed part of the cover where the winding is located, or, alternatively, the incorporation in the tire sidewall structure of electrodes to transfer the said power to a more suitable position for its use.
Another example is provided by U.S. Pat. No. 5,181,975, which describes a transponder supplied by a winding which is situated in the bead of the cover, and is separate from the bead core but inductively coupled to the bead core; the currents induced in the bead core by an external magnetic field which varies in a sinusoidal way induce, in turn, voltages in the transponder supply winding.
This location of the secondary winding (inductive antenna), like the location in the crown described previously, offers the advantage of always having a good inductive coupling to the primary winding (transmitter). However, this solution also presents problems in respect of both the mechanical characteristics of the tire (with a substantially inextensible turn housed in a particularly complex and partially deformable structural area, namely the bead area) and its manufacturing process.
U.S. Pat. No. 4,006,449, having the title xe2x80x9cInformation detector for a tire wheelxe2x80x9d, describes a system of supplying a sensor of tire operating parameters, such as internal pressure and/or temperature, consisting of a winding comprising a specified number of turns located on the edge of the rim in a radially inward position with respect to the axis of rotation of the wheel.
The winding is connected to a passive transducer (the sensor) which communicates with the interior of the tire, being located in the sealing cap of the air filling valve of the said tire. The said circuit receives an excitation signal induced by a first coil fixed to the chassis of the vehicle and connected to an alternating current source which is also fixed to the vehicle; the impedance of the said coil depends on the passive transducer, since the latter affects the strength and/or phase of the excitation signal.
A second fixed coil, inductively coupled to the turns of the rotating winding, senses the said variations of amplitude and/or phase and is connected to a circuit for processing the sensed signals, which controls both an indicator of the sensed values and any provided alarm devices which are activated in the presence of anomalous values of the parameters, such as a loss of pressure in the tire due to a puncture or fault in it.
This system would behave in a fairly satisfactory way, producing on the dashboard of a vehicle reliable information on the operation of the tires, combined with warnings of dangers due to anomalous situations, if it did not have an intrinsic weakness consisting in the flexible connections between the circular winding located on the rim and the transducer located within the cap of the air filling valve. These connections, being affected both by the centrifugal stresses caused by the rotation of the wheel and by the stresses due to the inevitable impacts of the wheel against accidental obstacles (when running over broken ground, pavements, etc.), are subject to frequent rupture.
U.S. Pat. No. 4,717,905, having the title xe2x80x9cWarning system including means for remotely energizing condition sensing devicexe2x80x9d, describes a system for remotely supplying at radio frequency one or more devices for sensing state conditions, such as the internal conditions of tires, wherein a radio signal generated by a radio-frequency source is received by a circular coil antenna installed on the rim of the wheel of a vehicle and is used to supply one or more transducers of physical values, for example pressure, connected to the antenna. The transducer varies the resonant frequency of the oscillating circuit comprising the antenna installed on the rim as a function of the value of the physical quantity which is being monitored; the variation of the resonant frequency is sensed by circuits associated with the radio-frequency generator and can then be used to control instruments and alarms on the dashboard of the vehicle.
The principal disadvantages of the described system are inherent in the geometrical and mechanical design of the system: the coil antenna mounted on the rim has to be electrically connected to the sensors incorporated in the tire, with the usual problems related to the low reliability of connectors which have to be incorporated in parts subject to large deformations, such as the structural components of tires.
The examination of the prior art as described above reveals that there is not yet available a simple and reliable electricity generator which is capable of supplying sensors of operating parameters of the tire or other devices and which does not use electrical connections, particularly those with equipment fixed outside the tire, with all the problems associated with them.
The applicant has now discovered that the bead cores of tires, being structural components which are always present both in tires with radial carcass and in those with conventional carcass, can be used advantageously as the core of a secondary inductive element. In particular, bead wires are usually made from steel wire or strip, in other words from ferromagnetic material and are therefore suitable for use as the core of a secondary inductive element. Furthermore, their magnetic permeability may be increased if necessary by the addition of suitable materials capable of increasing the linked magnetic flux.
The applicant has also discovered the use, as a primary inductive element, of a magnet or an electromagnet which is advantageously fixed to a support which is mounted on the hub of the wheel and is therefore in a fixed position.
The applicant has further discovered that the user circuits may also advantageously be mounted, with the secondary inductive element, on a structural member which is substantially free of large deformations, such as the reinforcing bead core of the bead.
The bead core is in fact the least deformable structural member of the tire and is therefore well suited for use as the base for mounting electronic devices for sensing and transmitting signals, these devices, owing to their rigidity, fragility and sensitivity, not being generally suitable for inclusion in elastomeric components subject to large deformations.
In a first aspect, the present invention relates to a tire for vehicle wheels, comprising a toroidal carcass provided with axially opposing sidewalls terminating in beads for fixing the said tire to a corresponding mounting rim, each of the said beads being provided with a reinforcing annular core, a tread band disposed on the crown of the said carcass and axially extending continuously between the said sidewalls, characterized in that at least one of the said annular cores is used as a ferromagnetic core and at least one turn of conducting wire is wound around the transverse profile of the said annular core to form a secondary inductive element of an electricity generator.
According to the invention, the said secondary inductive element can be associated with at least one primary inductive element to form the said electricity generator, the said primary inductive element and the said secondary inductive element being movable with respect to each other.
Preferably, the said annular core comprises a layer of material with high magnetic permeability. In an alternative embodiment, the said annular core comprises a plurality of blocks of material with high magnetic permeability.
In a different preferred embodiment, the said annular core is made from steel and comprises a matrix of the elastomer or plastomer type, either thermoplastic or thermosetting, containing soft ferromagnetic material in powder form.
Preferably, the said tire comprises electronic circuits supplied from the said secondary inductive element.
More preferably, the said electronic circuits comprise means for sensing certain parameters of the tire. In particular, the said electronic circuits are fixed to the said annular core.
Preferably, the said sensing means comprise at least one temperature sensor and/or at least one pressure sensor and/or a pair of extensometers, disposed in two orthogonal directions, which sense the deformations of the said annular core.
In particular, the said electronic circuits comprise data transmission means capable of transmitting the said parameters of the tire.
In another different aspect, the present invention relates to a system for sensing and signalling parameters of the physical state of a tire for vehicle wheels, mounted on a corresponding mounting rim, comprising a tire having a toroidal carcass provided with axially opposing sidewalls terminating in beads for fixing the said tire to the said rim, each of the said beads being provided with a reinforcing annular core, a tread band disposed on the crown of the said carcass and axially extending continuously between the said sidewalls, a device for sensing the said parameters of the physical state of a tire, and an electricity generator for the supply of the said sensing device, characterized in that at least one of the said annular cores is used as a ferromagnetic core and at least one turn of conducting wire is wound around the transverse profile of the said annular core to form a secondary inductive element of the said electricity generator.
Preferably, the said secondary inductive element can be associated with at least one primary inductive element to form the said electricity generator, the said primary inductive element and the said secondary inductive element being movable with respect to each other.
According to a preferred embodiment, the said primary inductive element comprises at least one permanent magnet. In an alternative form, the said primary inductive element comprises at least one electromagnet and at least one second turn of electrically conducting wire wound around the transverse profile of the said at least one electromagnet to form at least one primary winding of the said electricity generator.
In particular, the said electromagnet is supplied with direct current, or with alternating current, or with direct current and with alternating current.
In another different aspect, the present invention relates to a method for producing a tire, comprising the following steps:
producing on the preparation machines the semi-finished products required for building a tire, comprising a pair of ferromagnetic annular elements for fixing the said tire to a corresponding mounting rim;
forming a first secondary winding of an electricity generator, by disposing on at least one annular core of the said pair, called the annular coil element, at least one first turn of electrically conducting wire, wound around the transverse profile of the said annular coil core, and
assembling the said semi-finished products on tire building machines to form a green carcass for the said tire, comprising at least one annular coil core.
Preferably the step of forming the said first secondary winding comprises the step of fixing means for sensing certain physical parameters of the tire, supplied from the said power generator, to the said annular coil core.
In particular, the step of disposing a layer of material with high magnetic permeability on the circumference of the said at least one annular core while it is without the said one turn is carried out before the step of forming a first secondary winding.
In another different aspect, the present invention relates to a method for generating an electrical current within a tire for the supply of at least one electronic device, comprising the stage of inducing a variable magnetic field in a winding formed by at least one turn wound around a bead core belonging to the said tire.